The invention concerns a method for rolling thin and/or thick slabs made of steel materials into hot-rolled strip, which were previously cast as thin or thick slabs in a continuous casting machine, heated to rolling temperature in a pusher furnace or in a walking-beam furnace, and rolled in a rolling train, then cooled and wound into coils.
In general, only one and the same product is always produced in a rolling train, possibly with different dimensions, in the case of hot-rolled strip, with different widths or thicknesses. Efforts to increase the capacity utilization of a rolling train have resulted in the use of so-called “mixed rolling” since 2002, i.e., the rolling of significantly different strand thicknesses and strand widths. This has made it possible to lower the capital investment for a plant and the cost of the rolled product.
WO 02/068137 A1 describes a method for operating a continuous casting and rolling plant, in which a continuous casting and rolling plant is defined by the combination of the processes “slab casting” and “hot rolling”, which are otherwise separate in conventional steel plate production. Continuous casting and rolling is based on a slab production line (continuous casting machine) and a rolling train, in which a slab feeding device that is independent of the slab production line is provided. Several casting machines are necessary to achieve full capacity. A maximum possible production output is only possible either with a plant with two casting installations or with a twin-strand casting installation. Nevertheless, the rolling train always rolls faster than casting can be accomplished in a full casting operation. Unused production gaps arise from set-up times of the casting machine (tundish, mold or segment changes, and maintenance work). During production breaks in the slab production line, stored slabs can be fed into the rolling train to fill the production break. The stored slabs can only originate from a second continuous casting machine. In the production of thin slabs on a thin slab production line and in the production of thick slabs on a thick slab production line, a separate continuous casting machine is necessary for thin slabs and for thick slabs, and this in turn results in increased capital investment. Accordingly, the desired coupling of the continuous casting machine with a (finishing) rolling train also cannot be fully achieved in an economical way by means of two separate continuous casting machines for thin slabs and thick slabs or by means of a twin-strand continuous casting machine, because the higher investment costs are again reflected in the final product. However, the rolling of thick slabs in a separate roughing train is especially unfavorable. In this case, the hot-rolled strip is wound into coils after rolling, transferred in a coil box to a holding furnace, and fed from there to the finishing rolling train. This operating method results in higher production costs, loss of time and energy, and a reduction of production output. Therefore, in accordance with the state of the art, the only remaining option for increasing plant utilization is the filling of production breaks in the time intervals arising in the continuous casting machines. In this regard, only the specifically shorter rolling times relative to the specifically longer casting times can be utilized to increase the rolling train output.